Pump for Liquids Under Positive Pressure

ABSTRACT

A pump for liquids at positive pressure, includes a pump chamber ( 18 ) accommodating an impeller ( 24 ), wherein the impeller ( 24 ) is axially biased against a non-rotating support element ( 48 ) which determines the axial position of the impeller ( 24 ). The shaft ( 42 ) may be coupled to a drive shaft ( 64 ) through a magnet coupling ( 56, 62 ).

The invention relates to a pump for liquids under positive pressure,comprising a pump chamber which accommodates an impeller.

When pumping a liquid at a temperature above its boiling point, a highpressure must be maintained in order to prevent the liquid fromevaporating. Thus, for example, for hot water having a temperature of120° C., a pump must operate at a pressure of, for example, 0.25 MPa(2.5 bar), without any pressure losses. It can be assumed that, for anincrease in temperature of 10° C., the pressure must be increased byapproximately 0.1 MPa.

In order to maintain such a high pressure during operation of the pump,in case of an impeller-type pump, small tolerances must be provided forthe spacing between the impeller and the adjoining walls of the pumpchamber. If the play is increased by 1/10 mm, for example, the pressuremay be reduced by 0.1 MPa. On the other hand, a certain minimum spacingis necessary in order to limit the wear of the impelled which is mountedon a floatingly supported shaft. As a result, the allowable hot watertemperatures are limited by the increase of wear of the impeller.

It is an object of the invention to provide a pump of the type indicatedabove, which operates with as little wear as possible when pumpingliquids, and which at the same time permits to maintain a high pressure.

According to the invention, this object is achieved by the feature thatthe impeller is axially biased against a non-rotating support elementwhich determines the axial position of the impeller. Since the axialposition of the impeller is determined by the support element, thedimensions of the pump chamber and the impeller can be adapted oneanother with very high precision, so that a very small gap between theimpeller and the walls of the pump chamber can be maintained. Thus, forexample, the pump is suitable for pumping hot water at high temperaturesand at correspondingly high pressures.

Further developments and useful details of the invention are indicatedin the dependent claims.

Preferably, the impeller is fixed on a shaft which is axially biasedagainst the support element. Thus, a sliding rotary motion between theshaft and the support element occurs on a small radius, so that thefrictional resistance is reduced. For further reducing the friction, theshaft and the support element are preferably made of a ceramic material.

Preferably, the shaft is supported in at least one radial slide bearing.Accordingly, the radial position of the impeller can also be definedwith high precision. In order to reduce dynamic friction, the shaft andthe slide bearing are preferably made of a ceramic material. The shaftis displaceably supported in the bearing, so that it is possible toaxially bias the shaft and the impeller, respectively, against thesupport element.

Preferably, the support element and the at least one slide bearing areflushed with the liquid to be pumped, when the pump is operating.

Preferably, a flush passage passing through a wall of the pump chamberfor flushing the at least one slide bearing connects a pressure-sideregion of the pump chamber with a region situated beyond the slidebearing. In this way, the slide bearing can reliably be flushed with theliquid being pumped.

In a preferred embodiment, a flush passage for flushing the at least oneslide bearing is formed by a passage passing axially in the shaft. Thispassage may be provided in addition to the flush passage formed in thewall of the pump chamber.

Thanks to the flush passages according to the invention, the pump may beoperated not only with a horizontal axis of rotation of the impeller butalso in a suspended position, i.e. with a vertical axis of rotation ofthe impeller.

Preferably, a radial play between the impeller and the pump chamber isnot larger than 1/10 mm. This corresponds to an average distance betweenthe impeller and a wall of the pump chamber of 5/100 mm. It isparticularly preferred that the play amounts to not more than 5/100 mm,corresponding to an average spacing of 0.025 mm.

Preferably, an axial spacing between the impeller and the pump chamberon both sides of the impeller is not larger than 1/10 mm. Morepreferably, this spacing amounts to not more than 5/100 mm, particularlypreferred is a spacing of 3/100 mm or less.

The temperatures and pressures that are allowed for the pump accordingto the invention can be increased further, by dispensing with seals atthe rotating parts. According to a further development of the invention,the shaft is coupled to a drive shaft by a magnet coupling, wherein afirst coupling member of the magnet coupling is connected to the shaft,a second coupling member of the magnet coupling is connected to thedrive shaft, and a wall, which seals the drive portion of the pumpagainst a portion accommodating the shaft and the pump chamber of thepump, passes through a gap between the first and second couplingmembers.

By utilising the magnet coupling, seals at the rotating parts can bedispensed with, because no contact between the first and second couplingmembers occurs in the gap of the magnet coupling. Thanks to this, thepump may operate for example in a pressure range from 0.6 to 0.65 MPa,so that hot water at a temperature of 160° C., for example, may bepumped. Such temperatures are not allowable in conjunction withconventional rubber seals, for example.

It is particularly preferred that the first and second coupling membersare so arranged relative to one another that the magnet coupling urgesthe shaft axially against the support element. Thus, the magnet couplingfulfills two functions. On the one hand, it permits to seal the portionof the pump, which contains the liquid to be pumped, by a closed wall,so that no seals need to be employed at the rotating parts. On the otherhand, it assures that the impeller and the shaft, respectively, areaxially biased against the support element.

In another embodiment of the invention, the shaft is axially biasedagainst the support element by a compression spring. The compressionspring may also be used when a magnet coupling is provided.

Preferred embodiments of the invention will now be explained inconjunction with the drawings, wherein:

FIG. 1 is a partial section of a first embodiment of a pump having amagnet coupling; and

FIG. 2 is a partial section of a second embodiment of a pump having aslip-ring seal and a compression spring.

The pump shown in FIG. 1 has an essentially cylindrical casing 10 towhich an intermediate member 12 is flanged at the lower end thereof, anda head member 14 is flanged to the intermediate member. These membersare screw-tightened to the casing 10 by means of bolts 16 which passthrough the head member 14. In the intermediate member 12 and the headmember 14, a pump chamber 18 is formed, which extends between theintermediate member 12 and the head member 14 in the shape of aninterrupted ring and connects an intake passage of an intake pipe, whichhas not been shown, to an outlet passage 20 of an outlet pipe 22. In thesectional view shown in FIG. 1, the outlet passage 22 formed in theintermediate member 12 is positioned behind the plane of the drawing,whereas the intake passage, which has not been shown, is formed in thehead member 14 and is situated in front of the plane of the drawing.

The pump chamber 18 accommodates an impeller 24 having a disk-shapedcentral portion 26 and impeller blades 28, 30 which are arranged aboveand below the central portion 26 and each extend radially into an outerregion of the impeller 24. The blades 28 arranged above the centralportion 26, i.e. on the side of the outlet passage 20, are slightlydisplaced rearwardly in the direction of rotation of the impeller 24relative to the blades 30 provided below the central portion 26. Theblades 28 extend axially upwardly up to an upper face 32 of the impeller24. The blades 30 extend axially downwardly up to a lower face 34 of theimpeller. On the radially inner side of the pump chamber 18, the upperface 32 approaches a wall formed by the intermediate member 12 and formstherewith a gap of, for example, 2/100 mm, whereas the lower face 34approaches a wall formed by the head member 14 and forms therewith a gapof, for example, 3/100 mm.

The blades 28, 30 and the central portion 26 of the impeller 24 extendradially outwardly up to a straight outer periphery 36 of the impeller34. The outer periphery 36, in the range between the end of the pumpchamber 18 at the outlet passage 20 and the start of the pump chamber 18at the intake passage, has a lateral spacing of only 0.025 mm from awall that is formed for example by the head member 14. Thanks to thesmall lateral and axial spacings between the impeller 24 and thesurrounding walls, the pump is capable of maintaining a very highpressure.

The impeller 24 is fixedly mounted by means of a sleeve-type projection38 and by means of tolerance rings or corrugated rings 40 on a shaft 42that is made of ceramic material. Below the impeller 24, the shaft 42 issupported in a slide bearing 44 that is fixed in the head member 14 witha corrugated ring 46. The slide bearing 44 is made of a ceramicmaterial, e.g. silicon carbide.

At its lower end, the shaft 42 is slidingly supported on a ceramicsupport element 48 that is formed for example by a perforated disk oftungsten carbide and is fixed to the head member 14 with a bolt 50.

Above the impeller 24, the shaft 42 is guided in another slide bearing52 which is fixed at the intermediate member 12 with a corrugated ring54. The shaft 42 is slidingly guided in the slide bearings 44, 52.

A first coupling member 56 of a magnet coupling is fixed to the top endof the shaft 42 with a corrugated ring 58. The first coupling member 56extends in an annular shape around the end of the shaft 42 and issurrounded with a spacing by an annular flange 60 of a second couplingmember 62 of the magnet coupling. The second coupling member 62 is fixedat the lower end of a drive shaft 64 that is supported at the casing 10with a fixed bearing 66. The drive shaft 64 is driven by a motor of thepump.

A separating can 68 is arranged in a pot-shaped hollow space formedbetween the coupling members 56 and 62, the separating can having a verysmall wall thickness in the region of an annular gap 70 formed betweenthe first coupling member 56 and the flange 60.

The separating can 68 forms a wall made of a non-magnetic material, e.g.of VA steel. It is sealed against the intermediate member 12 with asealing ring 72, and the intermediate member 12 is again sealed againstthe head member 14 with a sealing ring 74. In this way, a closed hollowspace is formed, which encompasses the pump chamber 18 and is open onlyat the intake passage and the outlet passage 20.

At the annular gap 70, magnet elements 76 arranged in the first couplingmember 56 are opposed to magnet elements 78 that are arranged in theflange 60. They magnetically transmit a drive torque from the driveshaft 64 onto the shaft 42 and hence onto the impeller 24. The magnetelements 76 and 78 are axially offset relative to one another in such away that they exert an axial force onto the shaft 42, which urges andbiases the shaft 42 against the support element 48. In this way, theaxial position of the impeller 24 relative to the head member 14 andthus also relative to the intermediate member 12 is defined exactly, sothat, in spite of the very small axial spacings, no contact will occurbetween the impeller 24 and these members. For this reason, the pumpoperates with very little wear.

A flush passage 80 starts in the vicinity of the outlet-side end of thepump chamber 18, passes upwardly through the intermediate member 12 andopens in the region of the coupling member 56. The flush passage 80 isformed by a straight bore which is tapered at the lower end, so as tolimit the flow into the flush passage.

One purpose of the liquid that is driven upwardly through the flushpassage 80 is to flush the slide bearing 52. Moreover, this liquid isforwarded through a passage 82 in the form of an axial through-bore ofthe shaft 42 to the lower end of the shaft, where the liquid exitslaterally through grooves 84, that have been indicated in chain lines,and serves to flush the slide bearing 44.

The embodiment of the pump shown in FIG. 2 differs from the one shown inFIG. 1 especially by that it has no magnet coupling. Like or similarparts are designated by like reference numerals.

The impeller 24 is fixed on a shaft 86 with corrugated rings 40, theshaft 86 being supported at its lower end in the slide bearing 44 andbeing supported on the support element 48 like the shaft 42 in FIG. 1.At the upper end, however, the shaft 86 is reduced in diameter, passesthrough a bore 88 of the intermediate member 12 and is coupled to thedrive shaft 64 by a tappet sleeve 90. A gap between the shaft 86 and thebore 88 is sealed by a slip-ring seal 92 at a seal face 94. Via a sleevemember 96, the slip-ring seal 92 is pressed upwardly against the sealface 94 by a compression spring 98 the lower end of which is supportedon a shoulder of the shaft 86.

Since the shaft 86 is slidingly guided in the tappet sleeve 90, theslip-ring seal 92, the sleeve member 96 and the slide bearing 44, thecompression spring 98 will at the same time urge the shaft 86 downwardlyagainst the support element 48. In this way, the exact axial position ofthe impeller 24 relative to the head member 14 and the intermediatemember 12 is defined, similarly as in the first embodiment.

Again, the small spacings between the impeller 24 and the adjoiningwalls of the pump chamber 18, as mentioned above, are made possible bythe exact axial and radial positioning of the impeller 24. Thanks tothis, the pump operates with very little wear, and very hightemperatures and pressures of the liquid to be pumped are possible, inspite of the use of a slip-ring seal at the rotating shaft 86. Thus, forexample, it is possible to pump hot water at a temperature in the rangeof 120 to 130° C.

For flushing the slide bearing 44, a cross bore 100 is provided in thesleeve-type projection 38 and in the shaft 86 above the impeller 24, andthe cross-bore opens into a passage 102 formed by an axial bore of theshaft 86, through which liquid for flushing the slide bearing 44 isagain supplied from the upper portion of the intermediate member 12towards the lower end of the shaft 86, where it exits through thegrooves 84.

A vent and flush passage 104 extends in a height approximately below theslip-ring seal 92 from the upper portion of the head member 12 to theoutlet passage 20 and passes through a web 106 formed at the outlet pipe22.

The described embodiments of the pump have the outstanding feature thatthe constructions of the head member 14 and of the casing 10 and thedrive shaft 64 are identical, and that, in each case, the lower part ofthe pump comprising the intermediate member 12, the head member 14, theimpeller 24 and the shaft 42 and 86, respectively, can be removed formaintenance purposes. Further, this makes it possible to convert the oneembodiment of the pump into the other one by exchanging the lower partof the pump. The dividing line, where the exchangeable part is fitted tothe upper part of the pump, is always located outside of the range ofthe liquid to be pumped.

1. Pump for liquids at positive pressure, comprising: an impeller, atleast one pump chamber accommodating the impeller, a non-rotatingsupport element, and the impeller is axially biased against thenon-rotating support element which defines an axial position of theimpeller.
 2. Pump according to claim 1, further comprising a shaft whichis axially biased against the support element, and wherein the impelleris fixedly mounted on the shaft.
 3. Pump according to claim 1, furthercomprising at least one radial slide bearing which supports the shaft.4. Pump according to claim 3, further comprising a flush passage passingthrough a wall of the pump chamber for flushing said at least one radialslide bearing and which connects a pressure-side portion of the pumpchamber to a portion situated beyond the slide bearing.
 5. Pumpaccording to claim 3, further comprising a flush passage for flushingsaid at least one slide bearing and which is formed by a passage whichpasses axially through the shaft.
 6. Pump according to claim 1, whereina radial play between the impeller and a wall of the pump chamberamounts to not more than 1/10 mm.
 7. Pump according to claim 1, wherein,on both sides of the impeller, an axial play between the impeller and arespective wall of the pump chamber amounts to not more than 1/10 mm. 8.Pump according to claim 1, further comprising: a magnet coupling forcoupling the shaft to a drive shaft, the magnet coupling including afirst coupling member connected to the shaft, and a second couplingmember connected to the drive shaft, and a wall, which seals adrive-side portion of the pump against a portion accommodating the shaftand the pump chamber, passes through a gap between the first and secondcoupling members.
 9. Pump according to claim 8, wherein the firstcoupling member and the second coupling member are arranged in suchrelative positions that the magnet coupling biases the shaft axiallyagainst the support element.
 10. Pump according to claim 1, furthercomprising a compression spring which axially biases the shaft againstthe support element.